This invention relates generally to torsional vibration absorbers and relates, more particularly, to means for absorbing torsional vibrations and for reducing speed variations in a rotating shaft.
Shafts which are drivingly rotated commonly experience torsional disturbances during rotation, and these disturbances induce torsional vibrations in the shaft. In an internal combustion engine, for example, the engine crankshaft is exposed to cyclic torsional disturbances which tend to accelerate the shaft (during the power stroke) and which tend to decelerate the shaft (during the compression stroke). As another example, in a multi-blade grinding apparatus having rotating blades which are driven by a drive shaft, the drive shaft is exposed to cyclic torsional disturbances which tend to decelerate the shaft (upon impact of a blade with an object being ground) and tend to accelerate the shaft (upon recovery of the speed of the blade after impact).
The type of torsional disturbances with which this invention is concerned are those which are substantially regularly-spaced throughout a single rotation of the shaft. In a multi-cylinder internal combustion engine, for example, these torsional disturbances are a consequence of equally-spaced power pulses generated within the engine cylinders. For example, in an eight-cylinder engine, there are generated four equally-spaced power pulses, and thus four regularly-spaced disturbances for each revolution of the crankshaft. In a multi-blade grinding apparatus, e.g., a tree chopper, having shaft-driven blades which engage objects being ground at a predetermined number of equally-spaced intervals during a single revolution of the driving shaft, there are produced an equal number of regularly-spaced disturbances for each revolution of the shaft.
With regard to engine-driven shafts, it is known that the torsional vibrations induced in rotating shafts can be controlled, to a degree, with vibration absorber devices intended to oppose the forces which excite, and thus absorb, the vibrations. The operating principles of a vibration absorber are in contrast to those of a vibration damper which is intended to dissipate energy of the vibrations.
One vibration absorber is described in U.S. Pat. No. 2,346,972 as including a wheel, or auxiliary flywheel, which is attachable to the crankshaft of an engine and which is provided with a series of circular pockets that are regularly spaced about the center of the crankshaft. A cylindrical inertia member is positioned within each pocket so as to be free to move both radially and rotatively with respect to the wheel. During operation of the engine, the firing pulses of the engine rotate the wheel with the crankshaft and induce oscillatory movements in the inertia members which are intended to counteract the torsional crankshaft vibrations.
It is an object of the present invention to provide a new and improved system for absorbing torsional vibration and for reducing speed variations in a rotating shaft exposed to disturbances of the aforedescribed class.
Another object of the present invention is to provide such a system which absorbs torsional vibration and reduces speed variations in a rotating shaft at all shaft speeds.
Still another object of the present invention is to provide such a system whose design can be optimized without the need for time-consuming trial and error techniques.
Yet another object of the present invention is to provide such a system which is uncomplicated in construction and effective in operation.